Microelectromechanical systems (MEMS), for example, gyroscopes, resonators and accelerometers, utilize micromachining techniques (i.e., lithographic and other precision fabrication techniques) to reduce mechanical components to a scale that is generally comparable to microelectronics. MEMS typically include a mechanical structure fabricated from or on, for example, a silicon substrate using micromachining techniques.
The mechanical structures in MEMS devices are typically sealed in a chamber. The delicate mechanical structure may be sealed in, for example, a hermetically sealed metal container (for example, a TO-8 “can” as described in U.S. Pat. No. 6,307,815) or bonded to a semiconductor or glass-like substrate having a chamber to house, accommodate or cover the mechanical structure (see, for example, U.S. Pat. Nos. 6,146,917; 6,352,935; 6,477,901; and 6,507,082). In the context of the hermetically sealed metal container, the substrate on, or in which, the mechanical structure resides may be disposed in and affixed to the metal container. The hermetically sealed metal container also serves as a primary package as well.
In the context of the semiconductor or glass-like substrate packaging technique, the substrate of the mechanical structure may be bonded to another substrate whereby the bonded substrates form a chamber within which the mechanical structure resides. In this way, the operating environment of the mechanical structure may be controlled and the structure itself protected from, for example, inadvertent contact. The two bonded substrates may or may not be the primary package for the MEMS as well.
The sensitivity of a particular device is a function of the spacing between the electrodes in a device and the device element. A typical gap between the electrode and the device element may be on the order of 1 micron to 10 microns. Provision of a small gap is desired to increase the performance capability of the device. By way of example, the sensitivity of a particular device is proportional to 1/d2 wherein d is the width of the gap. Additionally, the power and voltage requirements for electrostatic actuation of the device are proportional to d2.
What is needed is a method of forming wafers such that the electrode spacing can be accurately determined. A further need exists for such a method which does not significantly increase the cost of producing the wafer. Yet another need exists for such a method which improves the antistiction performance of the device.